Exports for Node.js and Browserify

Has backwards compatibility for the old `require()` API. If we're in the browser, export as a standard global object.
ah nice, yeah that works. I guess the difference in their code they do have an "else" branch, but it's hard to infer the right pattern as they only add one variable to the global scope (whether observe-js *should* add so many names to the top level is another issue...)

anyway I'm fine with this code as is. Thank you!